Preheat the oven to 325 degrees. Line 2 large baking sheets with parchment paper (or use nonstick baking sheets). In a large bowl, sift together the flour, cocoa, baking powder, and salt. In a large bowl of an electric mixer, beat the butter and 1 1/4 cups sugar until light and fluffy. Beat in the eggs, one at a time, then add the lemon zest and liqueur. At low speed, add the flour mixture just until combined. Stir in the chocolate chunks and almonds.

Sprinkle a work surface with the remaining 1/2 cup sugar. Divide the dough in half. Roll each piece in the sugar into a 15-inch log. Arrange the logs, 3 inches apart, on 1 prepared baking sheet. Bake for 30 minutes or until center of each log is firm when gently pressed with a fingertip. Cool logs on the baking sheet 1 hour or overnight.

Preheat the oven to 300 degrees. Transfer the logs to a large cutting board. With a serrated knife, slice each log crosswise into 1/4-inch thick slices. Transfer the slices, cut-side down, to the baking sheets. Bake 12 to 15 minutes until crisp. Transfer the biscotti to wire racks and cool completely.